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several times in a raw on packaged rooftop units I couldn`t get down to 20*F compressor superheat although units were cooling and pressures were in the right ranges.I haven`t charged many rooftops yet.on residental split systems I didn`t have this situation.Is it not applicable to packaged units?thanks in advance.

Please to define what you intended to measure.
Where you made your readings.
How you made your readings.

Do you mean; superheat back at the compressor? Measured six inches from the suction service valve?
And you subtracted your suction line temp reading from your pressure gage reading, AFTER converting it from pressure to temperature?

So your saying that the heat load in the buildig is probably so great that the compressor is running flat out?
If the system is overloaded, then that is the reason there is no cooling back at the compressor!
That A/C system is working outside it design specs.

Possibly that tenant needs to add another A/C unit to their roof top.

A compressor will run without cooling. But not as well and not for as long.

Have you verified the system charge to be correct?

Have you thought about bring in a power washer to clean the condensor? Dont use it full strength. It needs to be the adjustable type of power washer. Otherwise you'd fold over all the fins. No bueno!

What is your subcooling while the system is operating? But of course, I dont know if you have a fixed orofice or TXV metering device.
That will make a difference too.

Originally posted by R12rules So your saying that the heat load in the buildig is probably so great that the compressor is running flat out?
If the system is overloaded, then that is the reason there is no cooling back at the compressor!
That A/C system is working outside it design specs.

Possibly that tenant needs to add another A/C unit to their roof top.

A compressor will run without cooling. But not as well and not for as long.

Have you verified the system charge to be correct?

Have you thought about bring in a power washer to clean the condensor? Dont use it full strength. It needs to be the adjustable type of power washer. Otherwise you'd fold over all the fins. No bueno!

What is your subcooling while the system is operating? But of course, I dont know if you have a fixed orofice or TXV metering device.
That will make a difference too.

Power washer..yes, after the condensor cleaner,a couple of times.One common problem I saw was bad fins already.Since my suction pressure came down to 60s I think it means the evap.can`t do any better.or it will start freezing.?so other than a little higher head pressure I didn`t concern with the fin conditions.

What's the temperature inside? If the load is as high as you say it is inside (Upper 70's? 80?) and your suction pressure is in the 60's, then there is probably either a slight undercharge or low airflow across the evaporator. What is the ambient temperature? Indoor Temp? Pressures?

Originally posted by dschwab9 What's the temperature inside? If the load is as high as you say it is inside (Upper 70's? 80?) and your suction pressure is in the 60's, then there is probably either a slight undercharge or low airflow across the evaporator. What is the ambient temperature? Indoor Temp? Pressures?

ambient temperature about 80*F,head pressure around 300 ,65 back pressure.inside lower80`s when I got there upper 70`s when I left.all coils cleaned and washed filters replaced.

Well, that's a really high head for 80 degree ambient. That's also a low suction for 80 degree return air. I'd suspect a restriction and the system has been overcharged trying to get the suction up, thus the high head and somewhat reasonable suction. What kind of metering device is it?

With the suction that low now, when the inside temp comes down to low 70's, you may start frosting the evaporator.